5 Jun 2008 ... Nuclear power is a viable alternative to carbon-based .... [9] D. R. Olander,
Fundamental Aspects of Nuclear Reactor Fuel Elements, National ...
Nuclear Fuel for Advanced Nuclear Fuel for Advanced Burner Reactors Alexander Thompson Alexander Thompson 6.5.2008
Nuclear Energy: Pros and Cons Nuclear Energy: Pros and Cons • N Nuclear power is a viable alternative to carbon‐based l i i bl lt ti t b b d energy – It has been pretty safe It has been pretty safe – It is ~0 CO2 – Mature technology
• There are some disadvantages – There is no long term solution for dealing with nuclear waste – Threat of nuclear proliferation
• Advanced Advanced burner reactors will be able to transmute burner reactors will be able to transmute transuranic elements produced in conventional light water reactors, turning waste into fuel
Great Let’ss Do it… Great Let Do it • Wait a minute i i – The behavior of this fuel is not well understood – Failure can occur because noble gases are very insoluble in nuclear fuels such as uranium dioxide • Th These atoms tend to segregate and form bubbles in the fuel, t t dt t df b bbl i th f l which eventually lead to macroscopic swelling and material degradation
• Processing of waste to use as fuel is tricky • Other design characteristics to worry about – High burnup
• It is expensive
• Let’s step through the process
Light Water Reactor‐ The Open Cycle Light Water Reactor The Open Cycle •
Mine of uranium ore Mine of uranium ore –
• •
Converted to uranium hexafluoride Gas centrifuge is used to sort the uranium isotopes – –
• • • • •
The uranium‐239 will decay into neptumium‐239 and will decay again into plutonium‐239
Ui Using water as a moderator the neutrons are slowed to become so called thermal neutrons d h l d b ll d h l – –
• •
High energy
If uranium‐238 absorbs a neutron, no more the chain reaction –
•
Chain reaction!!!
Th These neutrons are so called fast neutrons ll d f –
•
0.71% uranium‐235 0 71% uranium 235 LWR operate with 3.5%
Convert to uranium oxide (UO2) powder Powder is pressed into pellets and sintered Th The pellets are stacked in the reactor core ll t t k d i th t A neutron combines with a uranium‐235 atom making it a uranium‐236 Uranium‐236 spontaneously decays into fissile products and more neutrons –
•
Contains 0.1% U3O8
Low energy Less likely to interact with uranium‐238
The spent fuel has large amounts of uranium‐238, plutonium‐239, and even some uranium‐235 Th The current plan… t l
Yucca or BUST!
Yucca Mountain Yucca Mountain
Bust? • Limited capacity i i d i – As more nuclear power produced, need more Yuccas
• Yucca delayed – No current opening date!
• Store waste for thousands of years • Lots of opposition Lots of opposition • Large amount of material that could still undergo fission the spent fuel can be reprocessed in a fission, the spent fuel can be reprocessed in a closed cycle reaction
ABR The Closed Cycle ABR‐ The Closed Cycle • Global Nuclear Energy Partnership (GNEP) is a p g program to develop a closed fuel cycle p y – To address the security and environmental concerns about nuclear waste concerns about nuclear waste
• First step is to process waste from LWR
Waste Processing Waste Processing • • •
Aqueous Processing (UREX+, PUREX) Aqueous Processing (UREX+ PUREX) Pryrochemical Processing Iodine and technetium – Long half Long half‐lives lives Æ Æ Yucca Mountain Yucca Mountain
•
Cesium and strontium – Short half‐lives Æ low level waste repositories (10s of years) •
•
They would have to undergo decay storage until it could technically qualify
T Transuranic elements Æ i l Æ reprocessing for advanced burner reactor fuel i f d db f l
How to Turn Trash to Treasure How to Turn Trash to Treasure • Obviously need something more than LWR b i l d hi h • LWR used water as coolant and moderator – Thermal neutrons
• Need Need higher energy to transmute Np, Pu, Am, higher energy to transmute Np Pu Am etc. – Fast neutrons! Fast neutrons!
• Can not use a water coolant any more • Fast neutrons more likely to give p ( ) nonproductive reactions (U‐238) – Need higher enrichment
Sodium Cooled Fast Reactor Sodium‐Cooled Fast Reactor • Water around the core replaced with liquid sodium • Heat exchanger to a sodium loop • Heat exchanger to a H h water loop • Water turned to steam to turn a steam to turn a turbine
Failure • Fuel‐to‐cladding chemical interaction (FCCI) F l t l ddi h i li t ti (FCCI) – Eutectic melting between the fuel and the cladding
• U U, Pu, and La (a fission product) interdiffuse P d L ( fi i d t) i t diff with the iron of the cladding – The The alloy that forms has a low eutectic melting alloy that forms has a low eutectic melting temperature – FCCI causes the cladding to reduce in strength g g • Eventual rupture
• Noble gases are very insoluble in nuclear fuels – Segregate and form bubbles in the fuel • Leads to macroscopic swelling and material degradation
Noble Gas Atoms in U4O8 Noble Gas Atoms in U He, Ne, Ar, Kr, placed in the octahedral , , , ,p interstitial site of fluorite urania unit cell
Einc (eV) Einc (eV)
He
Xe
UO2 PuO2 AmO2 (Am0.5Pu0.5)O2
‐0.1 0.4 1.1 0.7
11.2 ‐ ‐ ‐
No ‘+U’, Nonmagnetic M. Freyss et al. Journal of Nuclear Materials 352 (2006) 144–150
Very large incorporation energies: consistent with lack of solubility of noble gases, y g p g y g , as well as previous calculations of Xe in UO2
Summary • Nuclear power is great l i – But serious drawbacks
• Closed cycle fission can alleviate issues of waste • Processing of waste is difficult • In the reactor, fast neutrons are used I th t f t t d – No moderator
• The environment is harsh and materials not well understood – Hard to model
References [1] Matt Krug, Guest Lecture from Northwestern Materials Science 395‐ [1] Matt Krug Guest Lecture from Northwestern Materials Science 395 Materials for Energy Efficient Materials for Energy Efficient Technology [2] “Nuclear Fission”, http://en.wikipedia.org/wiki/Nuclear_fission [3] U.S. Department of Energy, Global Nuclear Energy Partnership, http://www gnep energy gov/gnepAdvancedBurnerReactors html http://www.gnep.energy.gov/gnepAdvancedBurnerReactors.html [4] D. Hill, “Global Nuclear Energy Partnership Technology Demonstration Program”, Nuclear Physics and Related Computational Science R&D for Advanced Fuel Cycles Workshop, 2006 [5] J. J. Laidler, “The Advanced Fuel Cycyle Initiative of the U.S. Department OF Energy: Development of Separations Technologies , WM 04 Conference, 004 Separations Technologies”, WM’04 Conference, 2004 [6] M. J. Lineberry and T. R. Allen, Argonne National Laboratory “The Sodium‐Cooled Fast Reactor (SFR)” [7] George F. Vandegrift et al., “Designing and Demonstration of the UREX+ Process Using Spent Nuclear Fuel”, ATATLANTE 2004 [8] S. Bays, M. Pope, B. Forget, R. Ferrer, “Transmutation [8] S. Bays, M. Pope, B. Forget, R. Ferrer, Transmutation Target Compositions in Heterogeneous Sodium Target Compositions in Heterogeneous Sodium Fast Reactor Geometries”, INL/EXT‐07‐13643 Rev. 1, 2008 [9] D. R. Olander, Fundamental Aspects of Nuclear Reactor Fuel Elements, National Technical Information Service, Springfield Virginia, 1976 [ ] [10] N. G. Jensen, M. D. Asta, C. Wolverton, A. van de Waale, V. Ozolins, “Radiation Damage in Nuclear , , , , , g Fuel for Advanced Burner Reactors: Modeling and Experimental Validation”, a Research Proposal
Strain Due to Noble Gases (LDA) Strain Due to Noble Gases (LDA) *No O displacements*
Still insulating, no Still insulating no longer AFM Æ NM
• • • •
Interstitial Occupancy He Ne Ar Kr
E(U4O8Ng) –E(U4O8) E(Distorted U4O8)–E(U4O8) –E(Ng) (eV/unit cell) (eV/unit cell) 0.487 0.013 1.589 0.075 4.642 0.764 7.366
3.044
ΔE (Strained UO2) (eV/unit cell) 0.006 0.064 0.469
ΔE=K/2Vo*ΔV2 (eV/unit cell) 0.007 0.069 0.517
0.769
0.867
E(U4O8Ng) –E(U4O8) –E(Ng) Æ Energy of urania with interstitial gas atom minus the energy of pure urania minus energy of isolated gas atom E(Distorted U4O8)–E(U4O8) Æ Energy of injected urania with interstitial gas atom removed and the ions frozen minus the energy of pure urania ΔE (Strained UO2) Æ Energy of urania strained to equivalent volumes of urania with injected defects ΔE=K/2V / o*ΔV * 2 Æ Calculated energy of hydrostatically strained UO l l d fh d ll d h 2 with K=209 GPa
The effect of a gas atom in urania is not purely hydrostatic strain g p y y
Simple Model of Noble Gas Bubbles Simple Model of Noble Gas Bubbles
Noble Gas Impurities
UO2 Energetic Cost: Strain induced by Impurities i C S i i d db ii
Noble Gas Bubble
UO2 Energetic Cost: Creation of Bubble i C C i f bbl Energetic Gain: Relief of strain energy
At what point does the bubble become energetically favorable?
Energetics of Bubble Formation – Simple Model Simple Model Consider a Schottky defect as the smallest possible bubble Balance energy cost of Schottky vs. Strain relief of impurities Schottky defect volume ~ 40.4 Å3
He Ne Ar Kr
• • • • • • • •
Volume (Å3) 1.4 4.1 11.3 14 6 14.6
ΔE > Schottky Formation energy (~7.2 eV [+]) # Atoms/Schottky D. 29.8 9.8 3.6 28 2.8
E(U4O8Ng) –E(U4O8) –E(Ng) (eV) 14.543 15.498 16.569 20 281 20.281
We can do a “thought experiment” calculation to find the energy of a small bubble of gas atoms that fill a Schottky defect We take the volume of the Schottky defect as one fourth of the U4O8 unit cell We take the volume of the Schottky defect as one fourth of the U unit cell Take the ΔV between the pure oxide and the defect injected cell Calculate how many gas atoms will fit into the Schottky defect strain free (neglecting packing fraction, etc.) Multiply the number of atoms with the strain energy of an individual gas atom in UO2 This is the amount of energy recovered by allowing the gas atoms to cluster strain free The energy to create a Schottky defect is about ~7.2 eV [+] The critical number of atoms for nucleation of a bubble is very small – It may be more energetically favorable to create a Schottky defect and let the gas atoms cluster in a b i ll f bl S h k d f dl h l i lower strain environment [+]Gupta et. al. Philosophical Magazine, 87, No. 17, (2007), 2561–2569
